Nearly a month after a Google engineer released details of a new Windows XP flaw, criminals have dramatically ramped up online attacks that leverage the bug.

Microsoft reported Wednesday that it has now logged more than 10,000 attacks. "At first, we only saw legitimate researchers testing innocuous proof-of-concepts. Then, early on June 15th, the first real public exploits emerged," Microsoft said in a blog posting.

"Those initial exploits were targeted and fairly limited. In the past week, however, attacks have picked up."

The attacks, which are being launched from malicious Web pages, are concentrated in the U.S., Russia, Portugal, Germany and Brazil, Microsoft said.

PCs based in Russia and Portugal, in particular, are seeing a very high concentration of these attacks, Microsoft said.

Security vendor Symantec said these attacks peaked late last week. "Symantec has seen increased activity around this vulnerability. The increased activity started around June 21 and peaked around June 26 and 27," a company spokesman said on Wednesday. Attacks have leveled out since then, he added.

Criminals are using the attack code to download different malicious programs, including viruses, Trojans and software called Obitel, which simply downloads more malware, Microsoft said.

The flaw that's exploited in all of these attacks lies in the Windows Help and Support Center software that comes with Windows XP. It was disclosed on June 10 by Google researcher Tavis Ormandy. This Help Center software also ships with Windows Server 2003, but that operating system is apparently not vulnerable to the attack, Microsoft said.